Practical Steps in GC Troubleshooting

Transcription

1 Practical Steps in GC Troubleshooting Techniques, Tips, and Tricks Mark Sinnott Application Engineer GC Columns & Supplies Page 1

2 Everything was just fine and then this happened! How do I go about TROUBLESHOOTING? Page 3

3 Everything was just fine and then this happened! Logic = Something changed (slowly or sudden) = Something is different Track Events log book -Changed column, liner, septum, syringe, etc. -Injected samples, other method, etc. -Did maintenance, cut column, inlet flush, etc. Page 4

4 Logical Troubleshooting Troubleshooting Starts with Isolating the problem There are 5 basic areas from where the problem arises INJECTOR FLOW COLUMN DETECTOR ELECTRONICS But of course it can always be some COMBINATION Knowing what can & can t cause the symptom is the key Page 5

5 Typical Problems of Optimized Methods becoming Unoptimized and the Reason Why. Peak Tailing Flow Path or Activity Bonus Peaks In Sample or Back Flash (Carry Over) Split Peaks Injector Problems, Mixed Solvent No Peaks Wasn t Introduced, Wasn t Detected Response Changes Activity, Injector Discrimination, Detector Problem Peak Fronting Overload or Solubility Mismatch, Injector Problems Shifting Retention Leaks, Column Aging, Contamination or Damage Loss of Resolution Separation Decreasing, Peak Broadening Baseline Disturbances Column Bleed, Contamination, Electronics Noisy or Spiking Baseline Electronics or Contaminated Detector Quantitation Problems Activity, Injector or Detector Problems Page 6

6 Peak Tailing INJECTOR or COLUMN is Active -Reversible adsorption of active compounds (-OH, -NH, -SH) FLOW problem - dead volume, obstruction, poor installation, or severe column contamination Miscellaneous - overloading of PLOT columns, co-elution, polarity mismatch between phase, solute or solvent, and some compounds always tail *Tip = Inject a light hydrocarbon, should not tail unless flow path problem. Page 7

7 Bonus Peaks W h = Column: J&W P/N: Oven: DB-5 30 m x 0.53 mm I.D., 1.5 µm 60 C for 1 min C at 20 /min 300 C for 3 min Carrier Gas: Helium at 36 cm/sec Injector: Split 1:100, 250 C sample C 7 - C 20 Detector: FID, 250 C W h = Wh = Page 8

8 Bonus Peaks or Ghost Peaks Contamination in INJECTOR, COLUMN or FLOW (carrier gas) -Carry-over from a backflash or previous sample -Bad tank of gas or traps have expired -Septum bleed *TIP = Run a blank run it should be blank! Page 9

9 Page 10 Bonus Siloxane Peaks

10 GC Column Bleed Ions Page 11

11 Column Bleed is Influenced by: 1.3e4 1.2e4 1.1e4 Phase type Temperature Column dimensions 1.0e DB M x.53mm I.D., 3.0µm 24 pa / 260 C DB-1 30m x.32mm I.D.,.25µm 12 pa / 320 C Time (min.)

12 Split Peaks INJECTOR (poor sample introduction) -Injecting the sample twice (some how?) -Mixed sample solvent (polarity difference) -Sample in syringe needle (manual inject) INJECTOR (activity) -Breakdown (not really a split peak, 2 peaks) -Sample degradation in injector VOLATILITY High boilers dropping out on Cold Spots -Transfer line temps -Unions or fittings not tracking column temp Page 13

13 No Peaks DETECTOR (not on or not operational) INJECTOR (not working) -Plugged syringe/plunger not moving -Wrong injector (or detector) -Huge leak (older systems) -No carrier gas flow NOT the COLUMN Unless -Broken column or No column Page 14

14 Peak Response All Change in Size INJECTOR -Leaky syringe -Split ratio set incorrectly -Wrong purge activation time -Septum purge flow too high -Injector temperature too low* DETECTOR (response problem) -Settings or flows changed -Electronics failing *Tip = Ask is it all of them or some of them, if all then injector or detector Page 15

15 Peak Response Some Change in Size INJECTOR or COLUMN is active/contaminated -Irreversible adsorption of active compounds (-OH, -NH, -SH) -Decomposition of sample -Temperature Change Discrimination -Evaporation from sample *Tip = If only some change, then ask which ones? If active compounds then activity. If tracks volatility then cold spots or inlet discrimination. Page 16

16 Peak Fronting Shark Fin Shaped or Just Slight COLUMN (contaminated) -Overload (More pronounced with large solute and phase polarity differences) INJECTOR -Column installation -Compound very soluble in injection solvent (need retention gap) -Mixed sample solvent OTHER -Co-elution -Breakdown Page 17

17 Retention Time Shift INJECTOR -Leak in the septum -Change in injection solvent -Large change in sample concentration FLOW -Change in gas velocity COLUMN -Contamination -Damaged stationary phase -Loss of stationary phase -Change in temperature Page 18

18 Effect of Sample Overload on Retention Time and Peak Shape 1400 ng 7 ng min Page 19

19 Loss of Resolution Separation Peak Width Resolution is a function of separation and peak width Page 20

20 Loss of Resolution - Separation Decrease COLUMN -Different column temperature -Contamination (more phase?) Separation -Matrix components co-eluting -Different column phase? Peak Width Page 21

21 Loss of Resolution - Peak Broadening FLOW -Change in carrier gas velocity -Make-up gas Separation COLUMN -Contamination -Phase degradation Peak Width INJECTOR (efficiency) -Settings, Liner, Installation, etc. Page 22

22 Baseline Disturbances Sudden Changes, Wandering, or Drifting WANDER DRIFT COLUMN or DETECTOR -Not fully conditioned or stabilized (electronics) -Contamination FLOW -Changes in carrier and/or detector gas flows -Valves switching, leaks Page 23

23 Noisy Baseline MILD SEVERE FLOW -Contaminated gas -Incorrect detector settings COLUMN -Bleed if at high temperature -In detector flame (poor installation) DETECTOR -Air leak - ECD, TCD -Electronics malfunction Page 24

24 Spiking Baseline DETECTOR -Particles entering the detector -Random: poor connection -Regular: nearby "cycling" equipment (electronics) Page 25

25 Quantitation Problems DETECTOR -Poor stability (electronics) or Baseline disturbances (contamination) -Outside detector's linear range or wrong settings Activity (adsorption) in INJECTOR or COLUMN OTHER INJECTOR -Technique, settings, conditions -Syringe worn -Co-elution -Matrix effects -Sample evaporation leaky vials -Sample decomposition Page 26

26 What is NOT caused by a Column??? Peaks!! Any reproducible, sharp chromatographed peak! Siloxanes Degradation product peaks: Endrin Aldehyde, Endrin Ketone, DDE, DDD. Carryover of sample compounds Splitting of peaks Page 27

27 Troubleshooting Tools Bleed Profile: baseline problems Inject a non-retained peak: peak shape problems Test mix: all problems Isolate the components: all problems Condensation Test: baseline problems Jumper Tube Test: baseline problems Page 28

28 Generating a Bleed Profile 1.3e4 1.2e4 1.1e4 Produce when the column is new (for future reference) when there is a baseline problem 1.0e Time (min.) *DB-1 30m x.32mm I.D.,.25µm Temperature program // 40 C, hold 1 min // 20 /min to 320 C, hold 10 min. Page 29

29 Non-Retained Peak Shapes Used to Check Flowpath Good Installation Improper Installation or Injector Leak Potential problems: Injector or septum leak Too low of a split ratio Liner problem (broken, leaking, misplaced) Column position in injector and detector Page 30

30 Test Mix Used to determine how good the column is or if the problem is related to the chemical properties of the analytes. Test Conditions Inlet: Split (250 C) Detector: FID (320 C) Carrier Gas: Hydrogen Flow: 37.3 cm/sec (1.8 ml/min) Holdup Compound: Methane (0.671-min) Temperature Program: Isothermal at 110 C Page 31

31 Test Mixture Components Compounds Hydrocarbons Alcohols FAME s, PAH s Acids Bases Purpose Efficiency Retention Activity Retention Acidic Character Basic Character Page 32

32 Own Test Mixture More specific to your application Selective detectors Concentrations specific to your application Use same instrument conditions Easiest to simply inject a calibration standard Store for future measure of column performance Group/Prese Page 33

33 Isolate the Components Simplify the system: - example - Direct injection instead of P&T sample introduction Put in a known good column Move column to a different GC, inlet or detector Page 34

34 Condensation Test Used* to isolate the cause of: - Erratic baselines - Ghost peaks or carryover *Use when problems are worse after periods of GC non-use Page 35

35 Condensation Test Procedure Leave GC at C for > 8 hours Blank run Repeat a blank run immediately after the first blank run is complete Compare the two blank runs Page 36

36 Condensation Test Results First blank run is worse: - Contaminants (from injector, lines, traps or carrier gas) carried into the column Blank runs the same: contaminants are not strongly focused on the front of the column Page 37

37 Jumper Tube Test Purpose Helps to locate the source of contamination or noise Isolates GC components Page 38

38 Jumper Tube Test Isolate the Detector Remove column from the detector Cap detector and turn on Blank run Page 39

39 Jumper Tube Test Isolation of Detector - Results Detector OK Detector is the problem Page 40

40 Jumper Tube Test Isolate the Injector Connect the injector and detector meters deactivated fused silica tubing Turn on carrier gas Blank run Page 41

41 Jumper Tube Test Isolate the Injector - Results Injector OK Injector, lines or carrier gas contaminated Page 42

42 Jumper Tube Test Isolate the Column Reinstall the column Setup as before Blank Run Page 43

43 Jumper Tube Test Isolate the Column - Results Problem returns: It s the column Problem gone: Previous leak, solid debris, or installation problem Page 44

44 Page 45 And Now Let s do Some

45 Page 46 Troubleshooting-Example #1

46 A Real Troubleshooting Example 30 No Peaks Page 47

47 Logical Steps Taken to Find Peaks (most of our problems are leaks and plugs) Is the flame Lit? put glass piece over FID outlet----answer in this case, Water condenses look at output in instrument guage-- is the digital value greater than 0.0? Answer in this case is approximately 16.2 pico amps Is there flow through the column? disconnect column from detector and measure flow with bubble solution or meter Answer in this case was YES THERE IS FLOW Assess the observations Flame is lit and we have flow from end of column Hypothesis: Sample not getting on column-syringe plugged? Take syringe out and make injection manually on a dry paper towel Answer towel stayes dry (Syringe was clogged with septum) Pull plunger out top, add solvent and replace plunger will usually dislodge septum particle (should hear a little pop) If you can t dislodge plug, Replace syringe Reassemble the Injector & Re-inject Page 48

48 Peaks!! Page 49

49 Page 50 Troubleshooting-Example #2

50 8.0e4 7.0e4 6.0e4 5.0e DB-624 COLUMN 1. 1,2-Dichloropropane 2. Octane 3. Tetrachloroethylene 4. Chlorobenzene 5. Nonane 7.43 QC Test Mix Column: DB m x 53mm I.D., 3.0µm Carrier: Helium at 40 cm/sec measured at 35 C Injector: Mega Direct, 260 C Detector: FID, 300 C Oven: 35 C for 1.50 min 30 /min to 65 for 10 min 4.0e4 3.0e e4 1.0e Time (min.) Page 51

51 Example of Column Contamination 1.5e e4 1.3e4 1.2e DB-624 QC Test Mix* After 75 Injections of Oily Sample 1.1e4 1.0e Time (min.) *Temperature program// 35 C hold 1.50 min // 30 /min to 65 C, hold 10 min Page 52

52 Column and Liner Contamination Inlet coil of column Page 53

53 1.2e4 1.1e4 Example of Column Contamination 2.80 Removed 1 1/2 m from injector end * 1.0e Time (min.) *Before Column rinse and bake Temperature program // 35 C hold 1.50 min // 30 /min to 65 C, hold 10 min Page 54

54 Page 55 Looks Fixed Doesn't it?

55 Example of Column Contamination 1.3e4 1 1/2 mtrs removed* QC Test mix to Upper Temperature Limit 1.2e4 1.1e4 1.0e Time (min.) *Before Column rinse and bake. Temperature program // 35 C, hold 1.50 min // 30 /min to 65 C, hold 15 min // 20 /min to 260, hold 50 min Page 56

56 Backflush Column Rinse with 10ml each: Methanol, Methylene Chloride, Hexane Capillary column Special connector and ferrule Beaker for solvent collection 1/16" flexible teflon line to regulated pressure source Flexible teflon tubing Cap Capillary column Special adapter Vial Page 57

57 Jumper Tube Test Used to Isolate Source of Contamination. Cap off the detector and establish normal gas flows and temperature.. Plot the baseline using a temperature program. If flat.... Connect 1 meter of deactivated tubing between the injector and detector. Plot the baseline using a temperature program. If flat.... Install the column.. Plot the baseline using a temperature program. Page 58

58 1.0e4 Contaminated Inlet Jumper Tube Test* Time (min.) *1/2 mtr length of.53 mm I.D. deactivated tubing Temperature program // 35 C, hold 1.50 min // 30 /min to 65 C for 15 min Page 59

59 Rinsing Injector Carrier gas line GC Oven Injector body MeCl 2 C6 Page 60

60 Troubleshooting Tips 1. Isolate the problem. (Blank Run, Inject Un-retained Compound, Jumper Tube Test) 2. Change only one variable at a time. 3. Compare before/after chromatograms. (Peak shape, response, retention, baseline rise, background, look for trends, etc.) 4. Utilize Technical Support. Page 61

61 Remember Complete system = Carrier Gas + Injector + Column + Detector + Data System Multiple cause and effect Do not change too many variables at once Page 62

62 Contact Agilent Chemistries and Supplies Technical Support Option 3, Option 3: Option 1 for GC/GCMS Columns and Supplies Option 2 for LC/LCMS Columns and Supplies Option 3 for Sample Preparation, Filtration and QuEChERS Option 4 for Spectroscopy Supplies Available in the USA 8-5 all time zones gc-column-support@agilent.com lc-column-support@agilent.com spp-support@agilent.com spectro-supplies-support@agilent.com